1. Field of the Invention
The present invention relates to a pneumatic wrench, and more particularly to a pneumatic wrench having an enhanced structural strength to withstand a larger torque.
2. Description of the Related Art
A conventional pneumatic wrench in accordance with the prior art shown in FIGS. 6–8 comprises a pneumatic motor 10, a striking portion 20, and a drive shaft 30. The striking portion 20 is driven by the pneumatic motor 10 to rotate in the normal direction and the reverse direction to drive the drive shaft 30 to rotate, so that the drive shaft 30 is rotated to rotate a socket (not shown) mounted on the drive shaft 30 so as to drive and rotate a screw member, such as a bolt, nut or the like.
The pneumatic motor 10 includes a cylinder 11, a vane 12 mounted in the cylinder 11, a rotor 15 mounted in the cylinder 11, and a toothed shaft 16 mounted on and protruded outward from the rotor 15.
The striking portion 20 includes a support seat 21 having a first end face formed with a toothed hole 22 engaged with the toothed shaft 16 of the pneumatic motor 10 and a second end face formed with a through hole 23 for mounting the drive shaft 30, a first hammer 26 mounted in the support seat 21, and a second hammer 28 mounted in the support seat 21. The support seat 21 of the striking portion 20 has two opposite side walls formed with two mounting holes 24 for mounting two pins 25. The first hammer 26 and the second hammer 28 are fixed in the support seat 21 by the pins 25. Thus, the first hammer 26 and the second hammer 28 are driven by the pins 25. In addition, the first hammer 26 is formed with a first locking hole 27, and the second hammer 28 is formed with a second locking hole 29 located opposite to the first locking hole 27, so that the first hammer 26 and the second hammer 28 co-operate to drive the drive shaft 30 to rotate in the normal direction and the reverse direction.
The drive shaft 30 has a first end mounted in the support seat 21 of the striking portion 20 and formed with an engaging portion 35 engaged with the first hammer 26 and the second hammer 28 and a second end formed with a mounting portion 31 for mounting a socket (not shown). The engaging portion 35 of the drive shaft 30 has a first end formed with a first driven block 36 mounted in the first locking hole 27 of the first hammer 26 and a second end formed with a second driven block 37 mounted in the second locking hole 29 of the second hammer 28.
In operation, after the compressed air enters the cylinder 11 of the pneumatic motor 10, the vane 12 and the rotor 15 are operated to rotate the toothed shaft 16 which rotates the support seat 21, so that the support seat 21 of the striking portion 20 is rotated in the normal direction and the reverse direction to move the pins 25 to move the first hammer 26 and the second hammer 28 which are driven to strike the first driven block 36 and the second driven block 37 of the drive shaft 30 respectively, so as to drive the drive shaft 30 to rotate. Thus, the drive shaft 30 is rotated to rotate the socket (not shown) mounted on the mounting portion 31 of the drive shaft 30 so as to drive and rotate a screw member, such as a bolt, nut or the like.
However, both of the first hammer 26 and the second hammer 28 which are driven by the pins 25, so that the pins 25 are easily worn out or broken due to a stress concentration, thereby decreasing the lifetime of the conventional pneumatic wrench. In addition, the first driven block 36 and the second driven block 37 of the drive shaft 30 are respectively hit by the first hammer 26 and the second hammer 28 of the striking portion 20 constantly, so that the engaging portion 35 of the drive shaft 30 is easily worn out or broken during a long-term utilization.